If you had access to a time machine, what concerts would you go back to see?

Hendrix and Jefferson Airplane at Monterey Pop
Credence at Woodstock 
Any Zep before 1973
UFO with Michael Shenker 1978 Chicago
Ramones Rainbow Theater 1977
Rory Gallagher Montreux 1979
Ozzy with Randy Rhoads
Stevie Ray at the El Macombo 1983
Any thrash band in the Bay Area 1983

@Eonsx311, I attended the 5/23/94 Pulse show in Atlanta, which was indeed great. It is one of the far too few DVD's that I have that came from the same tour or the exact show I attended.....but, I also saw Pink Floyd on 6 - 23 - 73 in Detroit on the "DSOTM" tour. If I had to chose one, I'd probably have to go with the 73 show, because I remember far less of that show.

@laxiotakis, I agree that if I could only pick one music festival to go back in time to see, it would have to be the Monterrey Pop Festival. But, the Atlanta Pop Festival (aka Byron Pop Festival) would be a close second. Either way, you would have seen Jimi Hendrix. I have multiple friends who lived in Georgia at that time who could not go because they were too young to drive, and their parents wouldn't let them go.

@Ihasaguy, I caught the Beck - Bogart & Appice tour in 1973. That one was special. 

Early Zeppelin
Early SrV
Mid Stones
Late Hendrix
Anytime The Smiths